Prince Edward has pulled out of the Paralympics on the advice of the Government after Russia's decision to take military action in Ukraine.

The Earl of Wessex is patron of the British Paralympic Association and was due to attend the Sochi Games for three days next week but has now cancelled, Bucking ham Palace said tonight.

It marks a concerted effort by Britain to step up diplomatic pressure on Moscow after Russian President Vladimir Putin's decision to deploy troops to the former soviet state

Earlier, the Government announced it has withdrawn from preparatory talks due to be held in the coming days for the G8 summit in Sochi and ministers are boycotting the Winter Games.

William Hague, who has spoken to UN Secretary General Ban Ki-moon by telephone tonight, called for a "peaceful diplomatic" resolution to the crisis in Ukraine as he met leaders in Kiev for emergency talks.

The Foreign Secretary tweeted: " Have met a wide range of Ukrainian political leaders in Kyiv tonight. Violation of #Ukraine's sovereignty unacceptable

"Discussed with UN Sec General need for a peaceful diplomatic process to prevent escalation of #Ukraine crisis. UN has important role to play."

Ukrainian Prime Minister Arseniy Yatsenyuk has urged Russia to pull back its troops and warned "we are on the brink of disaster" as m asked gunmen continued to surrounded an infantry base in Privolnoye, Crimea.

US secretary of state John Kerry accused Russia of an "incredible act of aggression" and warned that it faces serious sanctions as well as risking its membership of the G8 group of leading nations.

Mr Cameron "remains gravely concerned" about the situation and has tonight talked to US president Barack Obama and premiers in Ukraine's neighbouring countries.

The Prime Minister said he and the US president agreed that Russia must face"significant costs" if it did not withdraw military forces.

He tweeted: " I spoke to @BarackObama tonight. We agreed Russia's actions are unacceptable & there must be significant costs if they don't change course."

A Downing Street spokesman said: "The Prime Minister and President Obama spoke at 9pm tonight.

"They agreed that Russia's actions were completely unacceptable. They agreed on the urgent need for de-escalation and for Russia to engage in a dialogue directly with Ukraine.

"They agreed there must be "significant costs" to Russia if it did not change course on Ukraine."